The invention relates to a metering pump having a predelivery chamber or diaphragm chamber, a pump cylinder and a metering piston co-operating with the pump cylinder. The predelivery chamber may be positioned above or laterally of the pump cylinder.
In conventional metering pumps having a metering piston-cylinder means and a predelivery diaphragm the predelivery chamber is connected with a metering agent tank through a suction conduit with a suction valve and a return conduit with a pressure valve. The metering agent is predelivered through the suction conduit and the suction valve into the predelivery chamber. The metering piston withdraws the required amount of metering agent from the predelivery chamber. The excess amount of metering agent is returned into the metering agent tank through a return conduit and a pressure valve. The metering piston emerges from the compression ring in the cylinder space for ventilation of the compression space. The repeated engagement or immersion of the metering piston into the compression ring causes a rapid mechanical wear of the latter which leads to high replacement expenses for such a cheap part as the compression ring.